The invention relates generally to latching levers for printed circuit boards and more particularly to an articulated latching lever.
It is conventional for printed circuit boards (PCBs) to be held in card holding frames so that the card contacts are inserted in mating connectors mounted on the frame. In order to obtain the necessary spacing from card to card, guide elements are provided which are secured to the frames in which the cards are slidably inserted. Since the mating connectors usually comprise a large number of connections, a substantial amount of force is necessary to provide for the insertion and removal of the mating portions of the connectors. The problem has been solved by providing the PCBs with one or more latching levers adapted to engage the PCB mounting frame to provide leverage thereby to reduce the amount of force to be exerted by a technician in the removal or insertion of a PCB in its frame.
Various prior art devices for performing this function are depicted in the following U.S. patents and attention is directed to them: U.S. Pat. No. 3,952,232 dated Apr. 20, 1976 to R. A. Coules, U.S. Pat. No. 3,798,507 dated Mar. 19, 1974 to N. F. Damon and H. G. Yeo; U.S. Pat. No. 4,064,551 dated Dec. 20, 1977 to R. Lightfoot; U.S. Pat. No. 4,313,150 dated Jan. 26, 1982 to Pak-Jong Chu; U.S. Pat. No. 4,233,646 dated Nov. 11, 1980 to E. C. Leung and I. R. Revah; and U.S. Defensive Publication No. T876,004 dated July 28, 1970 to J. Andreini et al. Another prior art device is pictured on pages 78 and 79 of the Fall 1975 Issue of Telesis published by Bell-Northern Research Ltd., Ottawa, Ontario, Canada.
All of these prior devices provide one or more latching levers for facilitating the removal, and in some cases, the insertion and retention of PCB connectors into and out of mating frame connectors.
For example, in the Lightfoot patent, a faceplate is secured to the front edge of a PCB. A pair of lever devices are mounted on the faceplate and the PCB. The latter is forced out by levering the faceplate away from the frame. If close packing of PCBs is paramount, it would seem appropriate to mount the levers directly to the PCBs thereby obviating the use of a faceplate. Such a device is disclosed in the Coules patent; however that device only assists in PCB removal.
Another example of prior art devices is described in the Telesis article identified above. In this case, the latching function is accomplished by a hooked portion of a lever that straddles the PCB and engages a pin mounted in the PCB. A handle, attached to the hooked portion of the device, enables the hooked portion to be disengaged from the pin thereby allowing the latching lever to pivot. The handle and hooked portion form one integral unit which is attached to the main body portion of the latching lever by a thin web of material. This thin web of material permits the latching lever to latch and to unlatch, but it is also a weak point in the latching lever in that the line of force, between the handle and the lever's pivot point, for pivoting the lever, is carried by the web. This problem is solved by the latching lever of the Leung et al patent which discloses a latching lever comprising a hooked portion flexibly connected to the body portion of the latching lever, an actuating member solidly connected to the hooked portion for moving the hooked portion relative to the body portion and a stop portion solidly connected to the body portion for limiting the movement of the actuating member. A stud carried by the PCB is engaged by the hooked portion of the lever to enable it to latch. Moving the actuating member disengages the hooked portion from the stud thereby unlatching the lever and leaving it free to pivot about its pivot point. Thus, the line of force, between the handle and the lever's pivot point, for pivoting the lever is carried by the stop portion and the body portion; it does not pass through the material by which the hooked portion is mounted to the body portion.
The present invention represents a radical departure from the known latching levers. The contemporary electronic equipment tends to be increasingly compact and one of the methods used to achieve compactness of packaging is to increase the depth of the shelves containing the PCBs. This packaging method allows the use of an additional set of PCBs mounted to the rear surface of the shelf backplane board. These PCBs are also held in card mounting frames including a faceplate and card guide elements mounted on the frame. The faceplate faces the rear of the cabinet and is usually adapted to receive connectors for interconnection of the shelf to other shelves and the outside world. Because of these connectors, the conventional known latches cannot be employed since they occupy or block off a large proportion of the faceplate.
The present invention solves this problem by providing a latch mechanism which, when operated, does not encroach on the space of adjacent shelves and in which the actuating member lies in a horizontal plane when the PCB is fully inserted in its slot.